In a synchronous direct-sequence code division multiple access (S-CDMA) system, users communicate simultaneously using the same frequency band via orthogonal modulation or spread spectrum. The number of orthogonal spreading codes (>1) limits the total capacity of the system. To increase the capacity of a CDMA system in a given service area, without requiring additional frequency bandwidth, space division multiple access (SDMA) can be employed.
In S-CDMA systems a set of orthogonal DS-CDMA codes are assigned to the cell of interest. However, the number of available orthogonal codes for a given spreading factor is limited, resulting in the capacity of the conventional S-CDMA system often being code limited.